An electrical power system is very complex. It needs some form of switch gear in order that it may be safely and efficiently controlled or regulated under both normal and abnormal operating conditions.A tumbler switch with a fuse serves to control the light and other electrical equipments and is,in a way a form of switch gear.On the other hand, a CB in Station serves exactly the same purpose but it has many added and much more complex features.
The basic construction of any CB Requires the separation of contacts in an insulation fluids which serves two functions.
1.It Extinguish the arc drawn between the contacts when the CB Opens.
2.It provides adequate insulation between the contacts and from each contact to earth.
Arc extinguishing ability: It should have a low dissociation temperature , short thermal time constant and should not produce conducting products such as carbon during arcing.
Commercial Availability at moderate cost:Of the simple gases air is the cheapest and most widely used for Circuit breaking.Hydrogen has better arc extinguishing property but it has lower dielectric strength as compared with air.Also if hydrogen is contaminated with air ,it forms explosive mixture. Nitrogen has similar as air , CO2 has almost the same dielectric strength as air but is a better arc extinguishing medium at moderate currents.Oxygen is a good extinguishing medium but is chemically active . SF6 has outstanding arc quenching properties and good dielectric strength.Of all these gases SF6 and air are used in commercial gas blast circuit breakers.
The basic construction of any CB Requires the separation of contacts in an insulation fluids which serves two functions.
1.It Extinguish the arc drawn between the contacts when the CB Opens.
2.It provides adequate insulation between the contacts and from each contact to earth.
Arc extinguishing ability: It should have a low dissociation temperature , short thermal time constant and should not produce conducting products such as carbon during arcing.
Commercial Availability at moderate cost:Of the simple gases air is the cheapest and most widely used for Circuit breaking.Hydrogen has better arc extinguishing property but it has lower dielectric strength as compared with air.Also if hydrogen is contaminated with air ,it forms explosive mixture. Nitrogen has similar as air , CO2 has almost the same dielectric strength as air but is a better arc extinguishing medium at moderate currents.Oxygen is a good extinguishing medium but is chemically active . SF6 has outstanding arc quenching properties and good dielectric strength.Of all these gases SF6 and air are used in commercial gas blast circuit breakers.
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